Thyroid disorders can have a significant impact on fertility in both women and men through several physiological pathways.
Here are the main causes concerning infertility related to thyroid dysfunction:
- Altered Peripheral Estrogen Metabolism
- Thyroid hormones influence the metabolism of sex hormones, including estrogen.
- In thyroid dysfunction, especially hypothyroidism, altered estrogen metabolism can disrupt the hormonal balance needed for ovulation and endometrial receptivity.
- This hormonal imbalance can lead to menstrual irregularities and anovulation, affecting fertility.
- Hyperprolactinemia
- Hypothyroidism leads to increased secretion of thyrotropin-releasing hormone (TRH), which stimulates prolactin release from the pituitary gland.
- Elevated prolactin levels (hyperprolactinemia) interfere with the secretion of gonadotropin-releasing hormone (GnRH), suppressing ovulation and causing infertility.
- Hyperprolactinemia can also lead to galactorrhea (milk production) unrelated to breastfeeding.
- Disturbances in GnRH Secretion
- Thyroid dysfunction affects the hypothalamic-pituitary-ovarian axis.
- Changes in thyroid hormone levels modulate GnRH pulsatility, which disrupts the release of luteinizing hormone (LH) and follicle-stimulating hormone (FSH), both crucial for normal ovarian follicle development and ovulation.
- These disturbances can result in anovulatory cycles or luteal phase defects, reducing the chances of conception.
Additional Impacts of Thyroid Dysfunction on Fertility
- Menstrual irregularities including oligomenorrhea (infrequent periods) and amenorrhea (absence of periods).
- Increased risk of miscarriage and pregnancy complications.
- In men, thyroid disorders can lead to abnormal sperm morphology and motility, contributing to male infertility.
Conclusion
Thyroid disorders, particularly hypothyroidism, contribute to infertility through mechanisms including altered estrogen metabolism, elevated prolactin levels, and disrupted GnRH secretion. Detection and management of thyroid dysfunction are essential components of infertility evaluation and treatment for improving reproductive outcomes.